ARCHIVED REPORTS_XR0004054 - Laserfiche WebLink

Home Browse Search

' eoo £c It T"hnics Inc, Page Glg Initial Site Conceptual Model Project No. 1030.2 June 18, 2003 7.0 FINDINGS AND DISCUSSION ' Samples collected during the installation of monitoring wells and the subsequent quarterly groundwater monitoring of the wells appear to indicate the presence of petroleum hydrocarbons released from the former UST. ' The site is located in the sediments of the Central Valley region. The water table wells are nnW-z _ =,t set in a claimer ich should impede the vertical migration of the plume. The clay may have a high cation exchange capacity (CEC) and the ionic attraction may slow the lateral migration of contaminates sorbed in the soil. The organic content of a soil can contribute ' substantially to the CEC and should be measured at the site. The current and potential threat to human health and safety is minimal. Site Characteristics • The plume is defined vertically by MW-101 and laterally by MW-2 and MW-3. • MW-4 appears to define the head of the plume. • The clay layer at 19 feet bgs provides a significant barrier to vertical plume migration. • Groundwater slope is gradual (<0.005 ft/ft), which minimizes the convective flow and impedes the migration of the plume. • Vertical slope is positive making downward migration unlikely. ' • Measurements of dissolved oxygen in the shallow monitoring wells range between 0.60 and 1.27 ppm. • Background wells MW-2 & 3, also exhibit very low dissolved oxygen of approximately ' 0.70 ppm, thus indicating the impact of the halo of reaction depleted water extends into that area. A nearly flat groundwater slope and soil, characterized by silts and clays,may have a positive contribution to natural biodegradation of contaminates at this site. ' 8.0 RECOMMENDATIONS GTI makes the following recommendations: ' ❑ Prepare and submit a Feasibility Study, discussing rernediation options for the Sinclair Trucking site (In progress). o Prepare a work plan to: o Further define the boundary of the plume o Install a downgradient monitoring well o Choose appropriate remediation activities. o Review tank pull reports. ❑ Continue quarterly groundwater monitoring.